Method and apparatus for determining location of an unknown signal transmitter

A system for determining the location of a signal transmitter transmitting a carrier signal from an unknown location, comprising:

• a receiver having an input for receiving the carrier signal emitted by the signal transmitter;
• a transmitter connected to the receiver for generating and transmitting an interrogation signal responsive to the carrier signal, the interrogation signal having a frequency offset from the frequency of the carrier signal, to the signal transmitter to be located in response thereto the signal transmitter generates and transmits an intermodulation return signal to the input of the receiver;
• a processor connected to the transmitter and receiver and responsive to the received and transmitted signals for determining the location of the signal transmitter;
• and
• said signal transmitter including a nonlinear output stage for combining the carrier signal and the interrogation signal to generate the intermodulation return signal.

A method for determining the location of a signal transmitter in relation to a transmitter locator, where said signal transmitter transmits a carrier signal from an unknown location, comprising the steps of:

• determining a bearing of the signal transmitter in relation to the transmitter locator, said step of determining a bearing further includes the steps of:
• receiving the carrier signal at the transmitter locator;
• and
• calculating the bearing of the signal transmitter from the frequency of the carrier signal;
• and
• calculating a range to the signal transmitter to the transmitter locator using an intermodulation return signal comprising a heterodyne combination of the carrier signal and an interrogation signal.

A method for determining the location of a signal transmitter in relation to a transmitter locator, said signal transmitter transmitting a carrier signal, comprising the steps of:

• receiving the carrier signal at the transmitter locator;
• calculating the bearing of the signal transmitter utilizing the frequency of the carrier signal;
• transmitting an interrogation signal generated by the transmitter locator in response to the carrier signal, said interrogation signal having a frequency offset from the frequency of the carrier signal;
• receiving the interrogation signal at the signal transmitter;
• mixing the interrogation signal with a selected harmonic of the carrier signal in the signal transmitter to generate and transmit an intermodulation return signal;
• receiving at the transmitter locator the intermodulation return signal;
• and
• calculating the range of the signal transmitter from the signal locator based on the round-trip time for the transmission of the interrogation signal from the transmitter locator until reception by the transmitter locator of the intermodulation return signal emitted by the signal transmitter.

A transmitter locator for determining the location of a signal transmitter having a nonlinear output stage transmitting a carrier signal, comprising:

• a receiver having an input for receiving the carrier signal emitted by the signal transmitter;
• a transmitter for generating and transmitting to the signal transmitter an interrogation signal responsive to the carrier signal and having a frequency offset from the frequency of the carrier signal, the nonlinear output stage of the signal transmitter to be located responds to the interrogation signal and generates and transmits an intermodulation return signal received at the input of the receiver, said intermodulation return signal comprising a heterodyne combination of the carrier signal and the interrogation signal;
• said nonlinear output stage further includes:
• a transistor for heterodyning the interrogation signal and the carrier signal to generate the intermodulation return signal, said transistor including a collector electrode;
• a wideband matching network having one input connected to the collector electrode of the transistor;
• and
• a low pass filter connected to a second input of the wideband matching network, the intermodulation return signal having an nth order component passing through the wideband matching network and the low pass filter;
• and
• a processor connected to the transmitter and receiver for determining the location of the signal transmitterr, said processor further includes:
• means for calculating the bearing utilizing the frequency of the carrier signal and either a beam forming technique or an angle of arrival technique;
• and
• means for calculating the range of the signal transmitter utilizing the round-trip time from the transmission of the interrogation signal until reception by the processor of the intermodulation return signal emitted by the signal transmitter.